Thermionic tube



Feb. 16, 1932.

F. S. M CULLOUGH THERMIONIC TUBE Filed Dec. 27, 1926 INVENTOR PatentedFeb. 16, 1932 UNITED STATES FREDERICK 8. MCGULLOUGH, F EDGEWOOD,PENNSYLVANIA THE'BMIONIG TUBE Application filed December 27, 1926.seriaim. 157,022.

8 According to the present invention, there emitting cathode is provideda tube wherein the anodes are entirely enclosed in a metal shell whichforms part of the cathode structure, and wherein there is providedinside the shell an adapted to be maintained at a temperature relativelyhigher than the temperature of the shell. The invention is particularlyapplicable to tubes used as rectifier's for alternating current.

The invention may be readily understood by referring to the accompanyingdrawings in which Figure 1 is a somewhat diagrammatic view illustratinga section through a thermionic tube embodying one form of my invention,

Figure 2 is a somewhat diagrammatic section illustratin another form ofthe invention and showlng only the electrode structure of the tube,

Fi ure 3 is a view similar to Figure 2, showing still another form ofthe invention,

Figure 4 is a horizontal section in the plane of line IV-IV of Figure3,'

Figure 5 is a View somewhat similar to Figure 3 showing anothermodification,

Figure 6 is a view similar to Figure 2 of still another construction,and Figure 7 is a diagrammatic view showing a circuit wherein a tubeembodying the present invention is used.

In the drawings, 2' designates the envelope of a tube having a stemportion 3 at the bottom thereof. Inside the tube is an inverted cupshaped metal cathode 4, whose bottom is closed by a plate 5, and whichis supported on wires 6' secured in the stem of the tube. One of thewires 6 is connected to a lead wire 7. Inside the shell or cylinder 4:is a heating element 8 having one end secured to the shell at 9 andhaving its other end passed through an insulating bushin 10 in the plate5. The lower end of this filament or heating element 8 is connected to alead Wire 11 which passes through the stem of the tube.

Inside the shell 4 are two anodes which may be of any suitable shape.They are represented as comprising plates 12 supported on wires. 13passing through insulated bushmgs 14; in the bottom plate 5. Each of thewires 13 is connected with a lead wire 15 passing through the stem ofthe tube.

In operation, a relatively low voltage current is connected across thewires 7 and 11 for heating the element 8 to a temperature sufiicient tomaintain electron emission. A relatively high potential is appliedacross the wires 7 and 15. The current applied to the wires 7 and 15 maybe the current to be rectified.

There is preferably maintained inside the vessel 2 a residuum of inertgas, preferably helium.

In the operation of the tube the wire 8 is maintained relatively hotwhile the remainder of the cathode structure, comprising the shell 1 andthe plate 5, are relatively cold. Rectification is accomplished in theusual manner, but the efficiency of the tube is very considerablyincreased over the efliciency of the usual hot cathode tube by reason ofthe surrounding shell 4, which, being charged similarly to the hotcathode 8 and which constitutes part of the cathode structure, tends todirect the entire electron flow toward the anodes 12.

In the arrangement shown inFi re 2, the structure is generally similarto t at shown in Figure 1, but in this modification the heater wire isenclosed in .an electron emitting cylinder. In this construction, 16designates the metal shell, 17 the bottom plate, 18 the heater wire and19 the anodes. Lead wires 20 are provided for the anodes and these wirespass through insulating bushings 21 in 99 the plate 5. Surrounding thefilament or heating wire 18 is a heat resisting insulating sleeve 22.Surrounding the sleeve 22, and in intimate contact therewith is anelectron emitting cylinder 23. This cylinder may be 5 provided with acoating of any suitable material, such as barium or strontium oxide, forgiving high emissitivity.

In the operation of the tube a source of heating current is connectedacross a wire 24 leadin to the cathode structure, and a wire 25 lea into one end of the heater 18. The other cm of the heater is connected tothe cathode structure, as shown. The current to be rectified is a pliedto the anodes 19 and to the wire 24. T e energization of the heator 18causes the temperature of the cathode 23 to be raised to a point whereelectron emission is sustained, and rectification 1s effected as in thestructure described in connection with Figure 1. The particularadvantage of this structure resides in the fact that a relatively largeemission surface 1s provided in the tube.

In the construction shown in F1gure 3 the general arrangement is againsomewhat similar to that described in connection w1th F gure 1, but inthis construction the he ater wire is not in series with the shell'as 1t1s 1n F1gures 1 and 2. In this figure, 26 designates the metal shell ofthe cathode structure, 27 the bottom plate and 28 is a metal sleevecentrally located in the shell 26. Th s shell 1s preferably coated onits exterior wlth a substance adapted to secure high electron emission.

Inside this sleeve is a rod of porcelain, quartz, or other refractory29. Passing through or embedded in'the rod 29 is a looped w1re 30through which a heating current is adapted to be assed. Lead wires 31and 32 are connected to the o posite ends of the heater wire 30, and oneof these wires is also connected to the cathode structure at 33.

Inside the shell 26 are two anodes 34 having lead wires 35 connectedthereto, these lead wires passing through insulating bushings 36 in thebottom plate 27. In this construction the cathode structure is shown asbeing .provided with two supporting wires 37,

neither of which constitute lead wires to the electrode. This structure,like that shown in Figures 1 and 2, can be mounted in a vessel having astandard four prong base. In the operation of the tube, heating @urrentis applied to the wires 31 and 32. One side of the rectifier circuit isconnected to the wire 32 and the other sides of the high voltage circuitconnect to the anodes 34 through wires 35 d Rectification is effected inthe usual manner, and the shell 26 functions to increase the efficiencyof the tube, as explained in connection with the structure shown inFigure 1.

The arrangement shown in Fi re 5 is general similar to that shown inT ire 3, but in this construction the heater or the cathode is reversed sothat the leads for the heater wire can be entered in the top of the tubeinstead of through the standard base. In this figure, 40 designatestheshell of the cathode structure, is a sleeve centrally located in theshell and having a porcelain or other refractory rod 43 entered thereinfrom the top of the shell. Embedded in the rod 43 is a heater wire 44 tothe opposite ends of which areattached lead 41 is the bottom plate, 42 7wires 45 and 46. These lead wires can ass through the top of the tube.Inside the s ell 40 at opposite sides of the sleeve 42 are anodes 47having lead wires 48 connected thereto, which pass throu h insulatingbushings 48' in the plate 41. The base for a tube having a cathodestructure of this nature would nee only three pron s. A wire .49 isconnected to the sleeve 42 or connecting the cathode in the rectifiercircuit.

In the arran ement shown in Figure 6 the shell of the cat ode-isdesignated 50, and 51 isthe plate for closing the lower end thereof.Mounted on a post 52 on the plate member 51, so as to be connected tothe plate member 51, is a thin metal sleeve 53 whose surface is coatedwith an electron emitting substance adapted to give a relatively highemission at comparatively low temperatures. A post 54 is secured to thetop of the sleeve 53 and the end of this post is connected to the upperend of a small coil spring 55 adapted to yieldably support the element53. The anodes 56 are arranged in the manner hereinbefore described inconnection with the other constructions, and have lead wires 57 attachedthereto which pass through insulating bushings 58 in the plate 51.

The construction shown in Figure 6 difiers from all of the otherembodiments herein disclosed in that there is provided no resistanceheated cathode. The cathode shown in this arrangement is capable ofsustaining electron emission when gaseous ionization occurs in the tubeupon the application of a high potential across the electrodes.

The tube is used the same as any ordinary rectifier tube. A rectifiercircuit, such as is commonly employed in the so called B batteryeliminators for radio purposes, is shown in Figure 7. In this figure, 6Odesignates the envelope of the tube, having anodes 61 and 62, a metalshell cathode 63, corresponding,

for instance, to the shell 26 of the structure shown in Figure 3, and anindirectly heated cathode element,64 having a resistance heater 65therein. The diagram in Figure 7 shows iagrammatically the type of tubemore fully illustrated in Figure 3. The cathode 64 is connected to oneside of a rectifier circuit 66 in which are included choke coils 67 foreliminating the A. G. ripple in the output circuit. The anodes 61 and 62are connected to the opposite ends of the secondary winding of atransformer, this secondary winding being designated 68.. The midpointof the winding 68 is tapped, as indicated at 69, and a wire 70 leadsfrom this tap and provides the other side of the rectifier circuit.Condensers 1 are connected across the wires 66 and 70 for the purpose ofminimizing the A. C. ripple. The primary for the transformer has notbeen shown, but such primary would be of the usual construction, andwould be inbe rectified. A small secondary winding 72 is illustrated forapplying a heating current to the heating element 65. y

In all of the embodiments herein illustrated, the tube is provided witha cathode structure comprising a relatively large shell and having arelatively small 'hot or electron emitting cathode entirely containedtherein. In each-case the hot cathode or electron emitting cathode isdirectl connected to the shell so that the shell an the emitting elementare always of the same potential, In each of the embodiments, the anodesare contained inside the shell so that a maximum of efii- 15 ciency isobtained. Due to the fact that a 7 hot cathode is em 10 ed and there isa rarified gas in the tube, t e rop across the electrodes is relativelylow as compared with some types of rectifier tubes. Furthermore, bycausing go the hot cathode and the anodes in the outer cold cathode orshell, the active gas is confined in a small space and flickeringbetween the hot cathode and the anode is prevented. The tube istherefore capable of giving a rela- 25 ti'vely heavy current in theoutput of the rectifier circuit.

While I have illustrated and described certain specific embodiments ofmy invention, it will be understood that these are merely an,illustrative of the invention, and that various modifications may bemade in the construction and arrangement of parts within thecontemplation of my invention and under the scope of'the following claimSI I claim A thermionic tube havin an inverted cup shaped cathode, a'late closmg the lowerend of the cup shape cathode, a central sleeve inthe cup shaped cathode adapted to form 40' an electron emitting element,said sleeve being connected to the shell, means projecting into thesleeve from the top of the cathode for heating the sleeve, anodesenclosed within the cathode, said anodes being provided with lead wireswhich pass through said plate, said lead wires being insulated from theplate. In testimony whereof I have hereunto set my hand. FREDERICK S.MOCULLOUGH.

